1. Field of the Invention
The invention relates to a guidance surface designed to carry an endless conveyor surface. It also relates to the belted or batten-type conveyors fitted with the said guidance surface.
2. Description of Related Art
The transfer of products in bulk from one place to another can be effected with different appliances, the choice of which depends on different parameters such as the distance transported, the volume to be transported per unit of time, and so on.
For the products in bulk, one is chiefly familiar with the endless-worm or belt-type conveyors. The endless worms are generally used over short distances while the belt-type conveyors are used over greater distances.
When these endless-belt conveyors are carrying bulk products, the active part of the belt must be shaped in a V or in U in order to constitute a sort of gully or trough containing the material throughout its journey. At the present time, in order to obtain this V or U shape, the belt runs sets of supporting rollers placed all along the trajectory. The geometrical position of the rollers on such an assembly determines the degree of concavity of the belt and therefore the desired profile.
In general, for this guidance assembly, use is made of a central horizontal roller and two or more lateral rollers which are sloped in relation to the horizontal so as to raise the edges of the endless belt.
When these conveyors are carrying granular materials, such as those present in ports or on sites for the extraction and transformation of granular materials, a part of the materials transported by the conveyor is transformed into airborne dust, and pollutes the environment.
The speed of movement of the belt increases the effects of the wind, and the quantity of material thus released is quite significant, particularly at the unloading docks of bulk carriers. These dusts have to be reduced.
One solution (FR-A-2.283.070) has been demonstrated by placing the active part of the belt in an enveloping cylindrical tube. This tube can be in a single piece or formed from assembled sections of tube. The belt slides in the tube, and it is the internal face of the tube which acts as the guide and geometrical shaper of the belt.
During the movement of the belt in the tube, two phenomena occur. The first phenomenon is the formation of a cushion of air between the carrying surface of the tube and the lower face of the belt. The belt is then effectively suspended. This avoids the use of a large number of rollers.
The second phenomenon is the formation of a current of air which carries most of the dust to the exit. With such a system, airborne dusts can thus be limited. In fact, the dust can escape from the tube only at the ends, where the means to monitor dust dispersion can be placed.
Unfortunately, this technology has a major drawback in the sense that dust is able to infiltrate between the belt and the carrying surface, and as it accumulates, it degrades the operation of the conveyor. This in turn leads shut-downs and cleaning operations. These shut-downs are very lengthy, since one has to remember that the belt is located inside a tube formed of tubular sections end to end, and that it can be relatively long. This renders it difficult to locate the trouble and deal with it. This also applies to maintenance work, which has to be performed regularly.